A belt transmission, which is continuously variable with respect to its transmission ratio, has a drive end, an output end and a primary valve for adjusting the transmission ratio and is, for example, known from DE 196 49 483 A1. The primary valve is driven by a control signal. A control circuit generates a control signal in dependence upon operating parameters of the vehicle transmitted to the control circuit. These operating parameters include, for example, the primary rpm, the secondary rpm and the position of the accelerator pedal.